The invention presented relates to an exoprosthesis/orthosis for the human knee-joint comprising an upper leg part which can be connected to the human upper leg as well as a lower leg part which can either be connected to the human lower leg or replace it, where both parts are connected to each other via at least one joint which constructs a joint with two joint axes, i.e. a dimeric joint chain, and carries out a constrained movement, such that both leg parts, with regard to their momentary joint axis, respectively have a corresponding curve path (movement or rest curve path).
An exoprosthesis for the human knee-joint is known from DE-OS 43 09 577. In this joint, the lower leg part and the upper leg part are connected by a four-joint arrangement formed by two parallel-arranged partial joints, namely a medial joint and a lateral joint, which each have the joint geometry of a joint chain with two joint axes (dimeric joint chain). The joint geometry of the medial joint is designed as an overlapping dimeric joint chain in which the joint axis of the lower leg part is displaced towards the direction of the upper leg part with respect to the joint axis of the upper leg part, and the joint geometry of the lateral joint is designed as an extended dimeric chain. Here, the joint axis of the lower leg part is displaced towards the direction of the lower leg with respect to the joint axis of the upper leg part. In each case, both the joint axes of the lateral joint and of the medial joint are connected to each other in an articulated manner by means of a coupling. With this four-joint design, a fixed, predetermined constrained movement of the lower leg with respect to the femur results, or vice versa. In the case of such a constrained movement of the lower leg part with respect to the upper leg part or vice versa, each respective joint part has a specific corresponding rest or movement curve path. The curve paths (rest curve path-movement curve path) are the curve paths on which lie the respective instantaneous centers of motion resulting from a continuous motion. The calculations for obtaining these curve paths are common knowledge.
It is the object of this invention, based on the known exoprosthesis/orthosis, to replace this with a simpler and more space-efficient construction.
This object is solved according to the invention by designing a curving toothed gearing section on both the upper leg joint section and the lower leg joint section whose teeth engage in the movement functional area of the joint, whereby the curved path of the gearing coincides with the curve paths of both joint sections in the movement functional area. Here, according to the invention, a four-joint arrangement is not imitated directly, but rather indirectly, as the rest curve path curve and movement curve path curve of the joint are approximated with gearing sections, which then, depending on their particular arrangement, engage with each other and thereby enable a counter-rotational encounter of the curve paths. The rest curve path in the reference system of the femur should be open ended at the bottom, and the instantaneous center of motion should move in a forwards direction from the extension to the bend. If the gearing path is matched to the respective curve path, a cam mechanism results, and the characteristic mechanism of a natural knee is nearly attained. The curve pair of gearings predetermines a constrained movement which rules out any slippage. In order to prevent the curved pair of gearings from becoming disengaged, the upper leg part and the lower leg part must be connected by a second joint connection (dimeric joint chain), comprising the joint axis found in the upper leg part, the joint axis found in the lower leg part, and a coupling located between these. In accordance with the invention, it can be advantageous if the curve paths are approximated by semi-circles whose middle points are used as joint axes. The joint section forming the femur (upper leg joint section) can thus, for example, be provided with an outer gearing, and the joint section forming the tibia (lower leg joint section) with an interior gearing, wherein the two gearings then engage with each other in the joint functional region. Design as a toothed gear segment enables a simple mode of production. If the middle points of the gears (approximate curve paths) or the gears"" axes of rotation are connected to each other via a coupling, the constrained motion of the system is guaranteed when forces are applied, that is, the geared joint sections are prevented from separating from each other since the coupling adds a load transmitting dimeric chain. In place of a separate coupling, however, a joint sheath can be provided, where the sheath sides serve at the same time as a load transmitting coupling.
Designing the invention as a geared joint results in a very compact version of the exoprosthesis which can also be produced economically.